Algae are unicellular organisms, producing oxygen by photosynthesis. One group, the microalgae, are useful for biotechnology applications for many reasons, including their high growth rate and tolerance to varying environmental conditions. The use of microalgae in a variety of industrial processes for commercially important products is known and/or has been suggested. For example, microalgae have uses in the production of nutritional supplements, pharmaceuticals, natural dyes, a food source for fish and crustaceans, biological control of agricultural pests, production of oxygen and removal of nitrogen, phosphorus and toxic substances in sewage treatment, and pollution controls, such as biodegradation of plastics or uptake of carbon dioxide.
Microalgae, like other organisms, contain lipids and fatty acids as membrane components, storage products, metabolites and sources of energy. Some algal strains, diatoms, and cyanobacteria have been found to contain proportionally high levels of lipids (over 30%). Microalgal strains with high oil or lipid content are of great interest in the search for a sustainable feedstock for the production of biofuels.
Some wild-type algae are suitable for use in various industrial applications. However, it is recognized that by modification of algae to improve particular characteristics useful for the aforementioned applications, the relevant processes are more likely to be commercially viable. To this end, algal strains can be developed which have improved characteristics over wild-type strains. Such developments have been made by traditional techniques of screening and mutation and selection. Further, recombinant DNA technologies have been widely suggested for algae. Such approaches may increase the economic validity of production of commercially valuable products.
For the production of some commercial products of interest, organisms producing the products may be grown in liquid environments. It is sometimes beneficial to remove the organisms from the liquid environments. One method of removing organisms is to flocculate or aggregate the organisms to facilitate removal. Flocculants or flocculating agents promote flocculation by causing colloids and other suspended particles (e.g., cells) in liquids to aggregate, forming a floe. Flocculants are used in water treatment processes to improve the sedimentation of small particles. For example, a flocculant may be used in swimming pool or drinking water filtration to aid removal of microscopic particles which would otherwise cause the water to be cloudy and which would be difficult to remove by filtration alone.
Many flocculants are multivalent cations such as aluminium, iron, calcium or magnesium. These positively charged molecules interact with negatively charged particles and molecules to reduce the barriers to aggregation. In addition, many of these chemicals, under appropriate pH and other conditions such, as temperature and salinity, react with water to form insoluble hydroxides which, upon, precipitating, link together to form long chains or meshes, physically trapping small particles into the larger floe.
Flocculation of microalgae using chemical flocculants is known. Long-chain polymer flocculants, such as modified polyacrylamides, are manufactured and sold by the flocculant producing business. These can be supplied in dry or liquid form for use in the flocculation process. The most common liquid polyacrylamide, for example, is supplied as an emulsion with 10-40% actives and the rest is a carrier fluid, surfactants and latex.
Use of chemical flocculants, however, has multiple drawbacks. For instance, use in water treatment and other processes require subsequent removal of flocculants. The addition and removal of flocculants adds to the cost of commercial production of a product of interest, thus decreasing the economic feasibility of production.